AQP2 and chronic kidney disease: Bearing in mind that AQP2’s role in CKD has not been fully established and that Tolvaptan has been shown to protect kidney function in advanced kidney disease but there are no studies at the early stages of kidney disease, this study aimed to evaluate if AQP2 expression is altered in an adenine-induced model of CKD in rats at early stages of CKD development (two weeks) and to assess a potential beneficial effect of Tolvaptan treatment.